Anhydrous ammonia applications shortly after corn planting can injure corn seedlings particularly under cold and dry soil conditions. Separating the corn seed/seedling by either time or distance from anhydrous ammonia applications helps to reduce the risk of injury. 

Anhydrous ammonia burn to corn

Anhydrous ammonia “burn” to corn roots occurs when the corn seedling comes into contact with high concentrations of free ammonia (NH₃). Anhydrous ammonia when injected into the soil is rapidly converted to ammonium (NH₄+) by associating with hydrogen ions. Most hydrogen ions come from water molecules and some come from soil cation exchange sites. When the hydrogen ions leave the water molecule, hydroxyl ions (OH-) are left behind. This reaction temporarily increases the soil pH at the point of injection and allows some free ammonia to exist in the soil which can cause injury or burn (Figure 1). High ammonium concentrations and high pH in the anhydrous band initially slow the conversion of ammonium to nitrate by soil microbes. When the ammonium undergoes nitrification, conversion of NH₄+ to NO₃-, the free hydrogen lowers the soil pH; therefore, the net effect of the anhydrous ammonia application is a lower soil pH. 

Anhydrous ammonia injury

Anhydrous ammonia injury to corn can occur over the ammonia knife track and result in poor corn emergence. This crop response can often be seen by following the direction of the anhydrous ammonia application through the field. Anhydrous ammonia injury results in uneven corn seedling emergence, slow growing plants, and seedlings may show wilting under dry soil conditions. Anhydrous ammonia injury is generally more pronounced in dry weather since injured corn seedlings have root systems that are slow to develop or become damaged “stubby” root systems that limit water uptake (Figure 2).

Related:Avian influenza detected in Utah

Even in dry soils, the conversion of ammonia to ammonium occurs rapidly. However, nitrification can occur relatively slowly when dry soils are also cool. Severely damaged roots turn black and may appear burnt. If injury to the corn stand is severe, replant decisions based upon the uniformity of the plant stand, date, and seed cost with re-planting as soon as possible.

Sidedressing with anhydrous ammonia can also cause injury by vapor damage to the leaves if ammonia escapes from applicator knives. If only a portion of the corn leaves are damaged, corn plants will usually grow out of the injury. There is no advantage in trying to sidedress anhydrous ammonia close to the corn seed. It is easier to inject anhydrous ammonia in the middle of the row. Corn roots will reach the middle of the row at approximately V8 with a 30-inch row width. 

Related:The trend is your friend

Preventing injury from anhydrous ammonia

Many factors determine the risk of ammonia injury. There are several guidelines that can help to minimize injury from anhydrous ammonia application prior to corn planting. 

Source: DeKalb Asgrow, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.